JPH09266079A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the failure of a circuit even when any one of contact pins of a discharge lamp touches a luminaire by adding one capacitor having an electrostatic capacity larger than that of a connected capacitor to a conventional circuit structure, and limiting its arrangement. SOLUTION: This discharge lamp lighting device has a commercial ac power source E; a full wave rectifier DS for rectifying a commercial ac power source voltage E; and a half bridge type inverter circuit for converting the rectified power source output to a high frequency power by use of high frequency switch elements Q1 , Q2 and supplying it to an ac load. The ac load forms a series circuit containing a discharge lamp FL, a ballast inductor L, and a first capacitor C2, and it further has a detecting circuit DET of the applied voltage of the discharge lamp FL. As improved points, a second capacitor C4 is inserted in series to the above series circuit, and the mutual arrangement of the three of the first capacitor C2, the second capacitor C4 and the discharge lamp FL is determined so that the capacitors C2 and C4 are situated on both sides of the discharge lamp FL.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device which prevents a short circuit to the ground potential when the discharge lamp is attached or detached, and thereby improves reliability and handleability.

2. Description of the Related Art FIG. 2 shows a conventional discharge lamp lighting device using a half-bridge type inverter. In the apparatus shown in FIG.
The commercial power supply voltage E is rectified by the full-wave rectifier DS, and the DC voltage smoothed by the capacitor C1 is switched by the switch elements Q1 and Q.
It is converted into high frequency power by 2 etc., and the high frequency power is supplied to the discharge lamp FL which is a load through the ballast inductor L. The capacitor C2 is a high frequency power supply capacitor for the half bridge circuit, and the capacitor C3 is a starting capacitor for the discharge lamp FL. Further, in the device of FIG. 2, an oscillation control circuit O for controlling the switching elements Q1 and Q2 is provided.
It has a tube voltage detection circuit DET for detecting the life of the SC and the discharge lamp FL, and both are connected to one end of the switch element Q2 which is the (−) potential of the half bridge circuit for ease of control.

The apparatus of FIG. 2 has the following problems. The discharge lamp FL may be attached or detached with the commercial power supply voltage E being applied. At that time, the upper or lower contact pin of the discharge lamp FL may touch the lighting fixture which is grounded to the ground potential. Now, assume that the lower contact pin in FIG. 2 contacts the lighting fixture. Since the lighting fixture is grounded to the ground potential at one end of the commercial AC power supply voltage E, ground-AC power supply voltage E-Fuse FU-Full wave rectifier DS-Discharge lamp FL lower pin-Upper pin-Lighting fixture-ground Closed circuit is formed. Therefore, the fuse F
The U may be blown out, or the parts such as the full-wave rectifier DS may fail. Next, it is assumed that the upper contact pin in FIG. 2 contacts the lighting fixture. In this case as well, almost the same as the above, but in this case, the upper contact pins are capacitors C2 and C3.
Since it is sandwiched between the two, almost no current flows, and there is no failure. It is an object of the invention to ensure that the circuit does not fail when either contact pin touches the luminaire.

A circuit configuration in which any contact pin of a discharge lamp is sandwiched by capacitors is provided. For this purpose, one capacitor is added, but the capacitance of the capacitor is made larger than that of the capacitor already connected. If the contact pins of the discharge lamp are always sandwiched between capacitors, no matter which contact pin touches the luminaire, an excessive current will not flow and the circuit will not fail. Also, if the capacitance of the added capacitor is increased, its voltage during normal operation will decrease,
It does not affect the operation of the tube voltage detection circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. The parts numbers in FIG. 2 are used as they are, and duplicate explanations are omitted as appropriate. In the apparatus shown in FIG. 1 as well, the DC voltage obtained by rectifying the commercial power supply voltage E by the full-wave rectifier DS is a switching element (switching transistor) Q1 · Q
It is converted into high frequency power by 2 etc., and the high frequency power is supplied to the discharge lamp FL through the current limiting inductor L. The capacitor C2 is a high frequency power supply capacitor for the half bridge circuit, and the capacitor C3 is a starting capacitor for the discharge lamp FL. Further, it has an oscillation control circuit OSC for controlling the switching elements Q1 and Q2 and a tube voltage detection circuit DET for detecting the life of the discharge lamp FL. In FIG. 1, the capacitor C4 is connected between the discharge lamp FL and (−) of the rectified DC voltage. Further, the capacitance of the capacitor C4 is set to be sufficiently larger than that of the capacitors C2 and C3. In FIG. 1, for example, when the contact pin on the lower side of the discharge lamp FL touches a lighting fixture connected to the ground potential,
The commercial power supply voltage E is applied between the lower contact pin-C4-DS-FU, but the capacitor C4 can protect the circuit because no current flows. Further, if the electrostatic capacitance of the capacitor C4 is made sufficiently larger than the electrostatic capacitances of the capacitors C2 and C3, the voltage applied to the capacitor C4 during normal operation can be made small enough not to affect the tube voltage detection circuit DET. it can. In this case, the rated voltage of the capacitor C4 is low enough. When the upper contact pin of the discharge lamp FL touches the lighting fixture, it is protected by the original capacitor C3. In the present invention, the arrangement of the capacitors C2 and C4 will be supplemented. In the above description, the existing capacitor is C2 and the capacitor C4 newly added according to the present invention is the capacitor C2.
This distinction does not have a heavy meaning because 2 · C4 has a serial relationship. For convenience of explanation, the capacitor C2 will be referred to as one capacitor, and the capacitor C4 will be referred to as a second capacitor. In the present invention, the first capacitor C2 and the second capacitor C
4. The mutual arrangement of the three discharge lamps FL is the first capacitor C2.
And the second capacitor C4 is located on both sides of the discharge lamp FL. In this way, either capacitor C2 or C4 functions as a protection element. The circuit can be protected regardless of whether the commercial power supply voltage E is on the low voltage side (installation side) or which contact pin of the discharge lamp FL touches the lighting fixture.

According to the present invention, when the discharge lamp is attached or detached in the state where the commercial power supply voltage is applied, even if the contact pin of the discharge lamp is accidentally touched with the lighting fixture, the circuit does not break down. It is possible to improve handleability.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a discharge lamp lighting device according to the present invention.

FIG. 2 is a circuit diagram showing a conventional discharge lamp lighting device.

[Explanation of symbols]

E: commercial power supply voltage, DS: full-wave rectifier, Q1 / Q2: switch element, L: current limiting inductor, FL: discharge lamp, C1 / C2 / C3 / C4: capacitor, OSC: oscillation control circuit, DET: tube Voltage detection circuit

Claims (1)

[Claims] 1. A half-bridge inverter circuit comprising a commercial AC power supply, a rectifying power supply for rectifying the commercial AC power supply voltage, and converting the output of the rectified power supply into high frequency power using a high frequency switch element and supplying the high frequency power to an AC load. Wherein the AC load has a series circuit including a discharge lamp, a ballast inductor, and a first capacitor, and the discharge lamp lighting device includes a detection circuit that detects an applied voltage of the discharge lamp, wherein Two capacitors are inserted in series, and mutual arrangement of the first capacitor, the second capacitor, and the discharge lamp is determined so that the first capacitor and the second capacitor are located on both sides of the discharge lamp. A discharge lamp lighting device characterized in that